What 1971 RPO was not available on a 429CJ equiped Car?
Winner gets a beer - must be at Bil’s Barret Jackson party to collect.
Sunroof?
NO - There are several XR7 429CJ sunroof cars on the registry. But good guess.
A 3 speed tranny.
Did someone say “tranny”?
LOL!!! 
Yeah, one of those, in a 3 speed.
Yessiree! we have ouselves our very own TRANNY watchdog!
As for the great question… what does RPO mean?
Regular Production Option
air conditioning?
Cruise control?
3spd - was standard cougar equipment - not optional.
Cruise control was not offered on a cougar 71-73
A/C was offered on hardtops.
Hint - it was an appearance option.
Since there are no more guesses here is the answer.
Wire wheel covers.
The 429CJ option required F70X14 tires belted traction tires, (or optional F60X15 inch tires)
The F70X14 inch belted tire came on a 14X7 inch steel rim or the optional 14X7 Kelsey Hayes styled steel wheel.
The wire wheel cover could not be ordered in combination with F70X14 belted traction tires. hence they were not available on a 429CJ Cougar.
Thanks for the guesses not for the tranny pictures.
Mitch
That was my next guess. 
Very interesting. Thanks.
Bill, what do you think about a trivia forum?
Drag pak??? I’m not sure why Ford did not allow the Mercury Cougars to have the 429 SCJ (with Holley carb) vs. the 429CJ…Only the Mustang got the SCJ engine
A small block engine was not available on a 429cj car 
True - but you couldn’t order, an AM/FM stereo and an AM/8Track ether - Nor could you order a blue vinyl top on your convert .
Wire wheel covers is actually listed as the one of item in the dealer book as an item that you could not order. Not an item percluded because you ordered something else i.e. you cannot have both a c-6 and an 4spd.
The other item was specific to the converts only was a/c. This was due to weight - it was determined with A/C they would have needed to upgrade to a G series tire which would have wheel clearance issues. - due to low anticipated demand for the 429CJ conv - you couldn’t order a/c - but since a/c was available on the HTs. The interesting note for the converts was that weight with a/c was an issue with cars with a C6 - technically the 4spd cars were just light enough to allow a/c but I think the factory didn’t want to deal with complaint about why can’t I get a/c with the automatic. After all if you rally wanted a/c - the dealer could instal it!